Field of the Invention
The present invention relates to a small-scale hydrogen liquefaction system equipped with a cryocooler. More particularly, the present invention relates to a small-scale hydrogen liquefaction system equipped with series-connected cryocoolers to increase a liquefaction rate to 10 L/h.
Description of the Related Art
Liquid hydrogen is used as a fuel. It is 10 times lighter than fossil fuels and is thus popular in the aerospace industry. That is, it is favorably used as a propellant for rockets, unmanned aerial vehicles (UAV's), etc. Furthermore, as vehicles that use hydrogen fuel in their internal combustion engine have been recently commercialized, there is a dramatic increase in the demand for liquid hydrogen as fuel.
This trend is boosting domestic demand for liquid hydrogen in fundamental research laboratories. Thus, supply of liquid hydrogen obtained through small-scale liquefaction can be an impetus for the development of relevant technologies and market expansion.
Meanwhile, a hydrogen liquefaction temperature is about 20.3 K. That is, hydrogen is liquefied at cryogenic temperatures unlike general materials. To obtain liquid hydrogen, various technologies including cryogenic engineering, thermodynamics, heat transfer, etc. are required. A typical large-scale hydrogen liquefaction plant involves a Brayton cycle or a Claude cycle, both of which need to use a variety of equipment such as a compressor, a heat exchanger, and a cryogenic turbine. Therefore, it is difficult to adopt such a cycle in a small-scale liquefaction process.
Therefore, different approaches are required to realize a small-scale hydrogen liquefaction system.
As a related art, Korean Patent No. 10-1585825 discloses a hydrogen liquefaction apparatus in which a heat pipe has a double pipe structure and a pre-cooling pipe equipped with an ortho-para converter is arranged in a double-piped portion filled with solid nitrogen (SN2). In the apparatus, gaseous hydrogen (GH2) sequentially undergoes pre-cooling and ortho-para conversion by passing through the pre-cooling pipe and the ortho-para converter and then comes into contact with an evaporator of the heat pipe, thereby being liquefied. This apparatus reduces initial loads of a cryogenic cooler in this way.
A conventional hydrogen liquefaction apparatus using a cryocooler has a disadvantage of small liquefaction capacity because it uses only a single pre-cooling pipe and a single cryocooler to liquefy hydrogen. Therefore, the conventional hydrogen liquefaction apparatus cannot meet an increasing demand for liquid hydrogen and cannot satisfy sufficient productivity and economic feasibility.
For this reason, development of a hydrogen liquefaction technology that can lower initial investment costs, simplify the structure of parts, guarantee safety, and increase a liquefaction rate to about 10 L/h is required.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.